The present invention relates to a resinous composition having a markedly increased flame retardance which comprises a magnet body powder and a polyolefin resin, containing a specifically combined use of a halogenated organic flame-retardant agent, antimony trioxide and zinc borate. More particularly, it is concerned with an exceedingly useful flame-retardant resinous composition having a high level of flame combustion resistance and a high level of glowing combustion resistance which is characterized by conjoint use of a halogenated organic flame-retardant agent, antimony trioxide and zinc borate hydrate in improving flame retardance of a polyolefin resin containing a magnetic body powder in large quantities.
A resinous composition prepared by mixing a large amount of a magnetic body powder with a synthetic resin is in widespread use as a plastic magnet. A composition using a polyolefin as the synthetic resin is especially useful because of cheapness and superior processability. In such plastic magnets an improvement of flame retardance has been recently needed in the electric and electronic applications. That is, materials satisfying both flame combustion resistance and glowing combustion resistance provided in so-called UL-94 Standard are strongly demanded. However, a known and general process for increasing flame retardance of polyolefin resins containing a magnetic body powder in a great amount by addition of common halogenated organic flame-retardant agents such as decabromodiphenyl ether, hexabromobenzene and "DECHLORANE (Registered trademark manufactured by Hooker Chemical And Plastics Corporation)" and antimony oxide is insufficient to provide the foregoing high level of flame retardance required for the practical usefulness. That is, by the foregoing process a high level of flame combustion resistance is achieved with relative ease but a resinous composition containing a large quantity of a magnetic body powder shows a tendency to have long glowing combustion time (called as glowing-time) that red-heated state lasts long even after a flame was blown out and thus practically satisfactory flame retardance is not obtained. In an attempt to solve these problems, a greater amount of flame-retardant agents is employed or fillers such as talc and the like are added but those are far from satisfaction in practical application on account of drawbacks including a decrease in mechanical strength of the final mold products as well as processability, an increase in cost and the like.